440 J. Neurosurg. / Volume 107 / August, 2007 N patients receiving extensive decompressive craniec- tomies, it is generally preferred to use the removed au- tologous bone flap for later reconstruction because of its mechanical, immunological, and aesthetic advantages. 4 Conventional methods of preserving the skull grafts have involved subcutaneous implantation in the abdomen, 2,7,12,17, 19,24,28,29 thigh, 3,20 or scalp. 8,10,22 However, this method of stor- age can cause patient discomfort and necessitates the cre- ation of a second incision site, thereby prolonging surgery and introducing the risk of postoperative complications such as wound infection at this second site. Alternatively, the bone flap can be cryopreserved alone, 5,9,18,26 sterilized in a steam autoclave prior to cryopreservation, 1,6,21,23,25 or immersed in hydrogen peroxide before EtO gas steriliza- tion with storage at operating room temperature. 16 Ethylene oxide sterilizes through its properties as a strong alkylating agent, reacting with proteins and nucleic acids in a tem- perature-dependent fashion to kill microorganisms. We de- scribe a simple and rapid technique for EtO gas sterilization of bone flaps, which has been used at our institution since 1996 and produces excellent aesthetic and functional re- sults in skull reconstruction and low overall infection rates. Materials and Methods Data Collection We retrospectively reviewed the medical records of 216 consecutive patients who underwent decompressive crani- ectomy for various indications between March 1999 (con- version to computerized medical records) and July 2005, as approved by the institutional review board protocol #2005- 0036. Of these patients, 103 eventually underwent cranio- plasty with autologous bone flap between May 1999 and October 2005 (Table 1). Five patients moved out of state during the follow-up period, and bone flaps were given to J Neurosurg 107:440–445, 2007 Ethylene oxide gas sterilization: a simple technique for storing explanted skull bone Technical note DAVID H. JHO, M.D., PH.D., 1 SERGEY NECKRYSH, M.D., 2 JULIAN HARDMAN, B.S., 2 F ADY T. CHARBEL, M.D., 2 AND SEPIDEH AMIN-HANJANI, M.D. 2 1 Neurosurgical Service, Massachusetts General Hospital, Boston, Massachusetts; and 2 Department of Neurosurgery, University of Illinois at Chicago, Illinois The authors evaluated the effectiveness of a simple technique using ethylene oxide (EtO) gas sterilization and room temperature storage of autologous bone grafts for reconstructive cranioplasty following decompressive craniectomy. The authors retrospectively analyzed data in 103 consecutive patients who underwent cranioplasty following decom- pressive craniectomy for any cause at the University of Illinois at Chicago between 1999 and 2005. Patients with a pre- existing intracranial infection prior to craniectomy or lost to follow-up before reconstruction were excluded. Autolo- gous bone grafts were cleansed of soft tissue, hermetically sealed in sterilization pouches for EtO gas sterilization, and stored at room temperature until reconstructive cranioplasty was performed. Cranioplasties were performed an average of 4 months after decompressive craniectomy, and the follow-up after reconstruction averaged 14 months. Excellent aesthetic and functional results after single-stage reconstruction were achieved in 95 patients (92.2%) as confirmed on computed tomography. An infection of the bone flap occurred in eight patients (7.8%), and the skull defects were eventually reconstructed using polymethylmethacrylate with satisfactory re- sults. The mean preservation interval was 3.8 months in patients with uninfected flaps and 6.4 months in those with in- fected flaps (p = 0.02). A preservation time beyond 10 months was associated with a significantly increased risk of flap infection postcranioplasty (odds ratio [OR] 10.8, p = 0.02). Additionally, patients who had undergone multiple craniot- omies demonstrated a trend toward increased infection rates (OR 3.0, p = 0.13). Data in this analysis support the effectiveness of this method, which can be performed at any institution that provides EtO gas sterilization services. The findings also suggest that bone flaps preserved beyond 10 months using this tech- nique should be discarded or resterilized prior to reconstruction. (DOI: 10.3171/JNS-07/08/0440) KEY WORDS • decompressive craniectomy • ethylene oxide • skull bone flap • sterilization I Abbreviations used in this paper: CT = computed tomography; EtO = ethylene oxide; OR = odds ratio; OSHA = Occupational Safe- ty and Health Administration; PMMA = polymethylmethacrylate; SAH = subarachnoid hemorrhage.